Several mutations have been found to be heterogeneous throughout cancer samples. As an example, approximately 20% of lung cancer cases have a mutation in the proto-oncogene RAS. In order to specifically test for heterogeneous mutations we introduce a new test that measures differences between quantiles. It will be shown that this test can achieve larger power values than a previously published test by Coombes et al. when sample sizes are small (10-20 samples) and the probability of mutation is small (10%-40%). When applied to two publicly available microarray data sets our method also produces lists of results that are 12% and 27% the size of those produced by Coombes et al.